A person is properly nourished who receives adequate energy in the form of carbohydrate and fat (and incidentally protein); adequate material for repair of wornout parts, such as protein and mineral salts; and the diet must contain certain accessory food substances known as food hormones or "vitamins." Also, it must contain water. But this is not all, for the food offered must be acceptable to the palate of the individual. A member of the French Scientific Commission which visited the United States in the summer of 1917, when questioned regarding the use of corn bread in France, replied "on ne peut pas changer des habitudes." The proper nutrition of an individual depends, therefore, not only upon a sufficient supply of food from a mechanistic standpoint, but also upon the reasonable satisfaction of the sense of appetite. These dual fundamentals of proper nutrition should be ever borne in mind.

Heat from the sun enters into the composition of the food substances when they are being built up in the plants, and this energy, which is latent in the food, is set free in the animal body and is used as the source of power behind all the physical activities of the body. The energy can all be recovered as heat and measured in the form of calories. According to the principles of the law of the conservation of energy, heat is not destructible. The understanding of the value of a calorie is indispensable for the comprehension of nutrition. A calorie is the measure of a unit of heat, or the quantity of heat necessary to raise a liter of water from 0° to 1° Centigrade. Apparatus has been invented for measuring the heat production of a man, an apparatus which is called a calorimeter or a measurer of calories. If one puts a man weighing, say, 156 pounds in the box of such an apparatus, so that he lies comfortably on a bed in complete muscular relaxation, and before his breakfast, one finds that he produces 70 calories an hour. Only in certain types of disease is there any variation from this normal, though of course the weight of the man makes a difference in his requirement for energy. If, at the same time the subject is in the box, the quantity of oxygen which he absorbs is measured and if certain other chemical analyses be carried out, one can calculate the exact amounts of protein, fat, and sugar which have been oxidized by this oxygen. Now, if one calculates how much heat ought to have been set free from the oxidation of these quantities of protein fat and carbohydrate, it is discovered that the heat which ought to have been produced is exactly that quantity which was measured as having been produced by the man. This measurement represents the basal metabolism of a man at complete rest, when his oxidative activities are at their lowest ebb.

The basal metabolism as measured by 70 calories per hour in the case of this individual represents the sum of the fuel needed—(1) to maintain the beating of the heart, which every minute of a man's life moves the blood or one-twentieth part of the weight of the body, in a circle through the blood-vessels; (2) to maintain the muscles of respiration that the blood may be purified in the lungs; (3) to maintain the body temperature at that constant level which is so characteristic that a slight variation signifies illness, and (4) to maintain in the living state the numerous tissues of the body. Any extraneous muscular movements are carried out in virtue of an increased oxidation of materials and the heat production rises above the level of the basal metabolism with increased muscular effort. For a long time the power for the maintenance of the human machine can be furnished by its own body fat, as is seen in cases of prolonged fasting, but usually the power is derived instead from the food-fuel which is taken. The great question in the world to-day is whether or not a sufficient quantity of food-fuel is available to support the human family. The question of calories is not an academic one, but an intensely practical one.

Science strives to express itself in mathematic terms, and this paper is written with that end in view.

Phenomena of life are phenomena of motion. These motions are maintained at the expense of chemical energy liberated in the oxidative breakdown of carbohydrate, fat, and protein. Furthermore, the protein structure of the body cells and the salts of the bones and other tissues are in a constant state of wearing down. The energy for the human machine and the materials for its self-repair are taken in the form of food. The general term metabolism includes all the chemical activities which take place under the influence of living cells.

The total quantity of heat produced by the body is a measure of the intensity of the oxidation of carbohydrate, fat, and protein within the body.

It is important to know definitely whether there is any constant measure of the level of the basal metabolism in normal people, so that one may determine in cases of disease whether the heat production is normal or increased or decreased.

Rubner discovered that the heat production of mammalia during rest was the same per square meter of surface whether the being was a horse, a man, a dog, or a mouse. The proposition has appeared so improbable as to call forth much antagonism. DuBois deserves the credit of having established this relationship for man beyond the possibility of a doubt. He was able to do this on account of his discovery of a new and accurate method of measuring the area of the body surface. It appears from his work that the basal metabolism for men between twenty and fifty years old is approximately 40 calories per hour per square meter of body surface, within a ± error of 10 per cent.

Boothby has found that the metabolism of patients who have recovered their health after hospital operations and who have been confined in the hospital between twenty and fifty days does not vary from the normal standard of DuBois.

It has been found by DuBois that the basal metabolism in boys of twelve is 25 per cent. higher than for an adult of the same height and weight, or 50 calories per square meter of body surface; and that in boys of fifteen the metabolism is 11 per cent. higher than for the adult of the same size and shape, or 44 calories per square meter of body surface (unpublished work of DuBois). These results explain the large appetites of boys.

Women show a metabolism which is 7 per cent. lower than that of men, or 37 calories per hour per square meter of surface.

From the charts of the average heights and weights of men varying between fifteen and fifty-five years old, given by American life insurance companies, Mr. H. V. Atkinson, of my laboratory, has calculated the basal metabolism in a table here presented. Unfortunately, the weights given in these statistics include clothes worn by the individuals. The calculated heat production, however, is in each case based upon the weight without clothes. The table is computed from the following values:

The table may also be used as follows:

THE BASAL METABOLISM OF MEN

Calculated from values of the basal metabolism determined by the methods of DuBois and applied to a table showing the average weights of 221,819 men of different ages and heights compiled from the statistics of the medico-actuarial investigation of 1912.

The basal metabolism of an average boy of thirteen years of age weighing 80 pounds and of a height of 4 feet, 10 inches, may be calculated as 1525 calories per day. This is the same as that of a man twenty-five years old, weighing 126 pounds and 5 feet, 2 inches tall.

A boy thirteen years old and weighing 156 pounds, his height being 6 feet, 1 inch (there are such cases), would have a basal metabolism of 2300 calories, or larger than that of any grown man given in the table—larger than a man weighing 211 pounds and 6 feet, 4 inches in height. I personally know a boy of this age and size. His parents are said to have sent him to boarding school in order to reduce their food bills.

It is evident from this discussion that the food requirement of boys over twelve years old is about the same as that of men. The emaciation of the children of the poor probably reduces their requirement of food. It is not generally recognized that the boy needs as much food as his father. The requirements of girls have not been investigated, but they probably need as much as their mothers.

These data will give with close scientific precision the minimal requirement for energy which is necessary for the maintenance of the bed-ridden.

Ordinary life, however, is not constituted after this fashion. "By the sweat of thy brow shalt thou eat bread."

From the work of F. G. Benedict one may calculate the increase in the basal metabolism, as follows:

If one wishes to determine from the basal metabolism table the heat production of a person who is confined to his room, one should add to the metabolism of the twenty-four hours the increase above the basal for those hours of the day during which he is sitting in a chair or standing.

Passing to a consideration of the subject of mechanical work done by a man, one finds that it requires about 1.1 calories to transport a pound of body weight three miles during an hour, and that increasing power must be generated if the speed is increased above this rate of maximal economic velocity.

These relations are shown below:

If one wishes to determine the heat production of a man weighing 156 pounds and 5 feet, 7 inches in height, and who is walking or running, the following calculations can be made:

If the man's food cost 10 cents a thousand calories, it may be calculated that he would have to walk over eight miles at a rate of three miles per hour in order to save money when he pays a 5-cent carfare. (This, however, does not include the cost of shoe leather.)

The carrying of a load of 44 pounds is done at the same expenditure of energy as the carrying of one's own body weight when the rate is three miles an hour, so the soldier's equipment would call for the added expenditure of 48 calories (44 × 1.1), making his total hourly expenditure of energy nearly 300 calories (249 + 44) during a hike on a level road. His daily requirement for energy might be:

This would be the heat production of a soldier on a day of a "forced march." The ordinary day's march is only fifteen miles.

This assumes a level road. If, however, there are hills to climb and the body weight and the pack are lifted 1000 feet during the hike, this is done at the additional expense of approximately 0.96 calory of energy per pound of weight lifted. If the man weighed 156 pounds and the pack 44 pounds, the additional fuel requirement would be 192 calories (200 × 0.96). The total energy requirement for this kind of a hike would have been 4200 calories. Walking down hill is accomplished at an expenditure of slightly less energy than walking on the level, but this factor need not concern one.

Supposing, however, this individual were running, lightly clad, on a level road in a race for a distance of 40 miles at the rate of 5.3 miles per hour, he would complete the distance in seven hours and thirty-three minutes, which is a reasonable record. His metabolism might thus be calculated:

It is a matter of record that a man has run between Milwaukee and Chicago, a distance of 80 miles, in about fifteen hours. Such an amount of work would have required over 9000 calories for the day.

These calculations are all based upon experimental results obtained in various laboratories in different parts of the world and can be accepted as being free from any gross error.

It is evident that the energy requirement is proportional to the amount of mechanical energy expended.

One may turn now to the fuel needs in terms of calories in certain industrial pursuits. According to Becker and HÄmÄlÄinen, the quantity of extra metabolism per hour required in various pursuits is as follows:

To use this table one may seek the basal metabolism of the individual, add 10 per cent. for sixteen hours of wakefulness when the person is sitting or standing, and then multiply the factors in the last table by the numbers of hours of work. For example, if one takes the individual weighing 156 pounds, one obtains the following requirements of energy if his business were that of a tailor and he worked eight hours a day:

After this fashion one might calculate his food requirements had he followed occupations other than that of tailor:

These figures make no allowance for walking to or from the place of employment.

The data here given are inadequate to cover the industrial situation, but they show clearly that heavy work cannot be accomplished without a sufficient amount of food-fuel.

The food-fuel with which to accomplish work is necessary not only for the soldier, but for the workman behind the line, and it should be adequate in quantity, satisfactory in quality, and not exorbitant in cost.

In virtue of the world-wide scarcity of food, the work of the individual should be worthy of the food which he eats.

Tables showing the cost of various wholesome food-stuffs about July 1, 1917, are here reproduced for the benefit of the reader. The tables were prepared by Dr. F. C. Gephart and issued by the Department of Health of the City of New York in a leaflet edited by Doctors Holt, La Fetra, Pisek, and Lusk on the subject of food for children. If the world is seeking after energy in the form of food-fuel, the world is rightly entitled to understand the value of its purchases. It must be clearly understood that people are always destined to look with hopeful anticipation toward the enjoyment of a meal. They will instinctively "eat calories" just as they instinctively "eat pounds." They buy pounds of food, and they could buy more intelligently if they knew the energy value of what they buy.

A British scientific commission has reported to Parliament that if the workman be undernourished he may, by grit and pluck, continue his labor for a certain time, but in the end his work is sure to fail. It makes no difference what the nutritive condition of the person is, if a certain job involving muscular effort is to be done it always requires a definite amount of extra food-fuel to do it. Rubner, the greatest German authority on nutrition, excited grossly inappropriate hilarity in the comic press of his country by showing that a poor woman who waited several hours in line in order to receive the dole of fat allowed her by the government actually consumed more of her own body fat in the effort of standing during those hours than she obtained in the fat given her when her turn to receive it came at last.

A method by which food-fuel can readily be saved with benefit to the nation and to the individual is for the overfat to reduce their weight. This has been done with drastic severity in Germany. I have heard from unquestioned sources how a man who had weighed 240 pounds lost 90 pounds since the war began; how a corpulent professor at Breslau lost greatly in weight, but during the second summer of the war regained his former corpulence during a sojourn in the Bavarian Tyrol, a joy not now tolerated; and how an American woman lost 40 pounds in weight last winter in Dresden. There is every reason why a man who is overweight at the age of fifty should reduce his weight until he reaches the weight he was when he was thirty-five. According to Dr. Fisk he is a better insurance risk if after thirty-five he is under the weight which is the average for those of his years. Reduction in weight reduces the basal requirement for food, and reduces the amount of fuel needed for moving the body in walking. The most extreme illustration of the effect of emaciation upon the food requirement is afforded by a woman who after losing nearly half of her body weight was found to need only 40 per cent. of the food-fuel formerly required. This represented a state not far from the border line of death from starvation, but it indicates how a community may long support itself on restricted rations. It must be strictly borne in mind, however, that if any external muscular work is to be accomplished it can only be effected at the expense of a given added quantity of food-fuel, whether the person be fat or thin.

It is not at all difficult to reduce the body weight. Suppose a clergyman or a physician requires 2500 calories daily in the accomplishment of his work and takes 2580 calories per day instead. The additional 80 calories is the equivalent of a butter ball weighing a third of an ounce, or an ounce of bread or half a glass of milk. It would seem to be the height of absurdity to object to such a trifle. But if this excess in food intake be continued for a year, the person will gain nine pounds and at the end of ten years ninety pounds. Such a person would find that he required a constantly increasing amount of food in order to transport his constantly increasing weight. In instances of this sort a motto may be applied which I heard the last time I was in Washington: "Do not stuff your husband, husband your stuff."

Now it is evident that, if instead of taking more than the required amount of food a little less be taken than is needed, the balance of food-fuel must be obtained from the reserves of the body's own supply of fat. By cutting down the quantity of fat taken, or by eliminating a glass of beer or a drink of whiskey, and not compensating for the loss of these by adding other food stuffs, the weight may be gradually reduced. The amusing little book entitled "Eat and Grow Thin" recommends a high protein and almost carbohydrate-free diet for the accomplishment of this purpose, but its advice has made so many of my friends so utterly miserable that I am sure in the end it will counteract its own message.

The work of the world is accomplished in largest part by the oxidation of carbohydrates, that is to say, of sugars and starches. Bread, corn, rice, macaroni, cane-sugar, these are par excellence the food-fuels of the human machine. In the dinner-pail of the laborer they testify as to the source of his power. They are convertible into glucose in the body, which glucose gives power to the human machine. They may be used for the production of work without of themselves increasing the heat production of the worker, as happens after meat ingestion. (See p. 18.) Fat also may be used as a source of energy, but unless carbohydrate is present a person can not work up to his fullest capacity.

Cane-sugar is a valuable condiment, and when taken in small quantities every half hour, may delay the onset of fatigue. It is more largely used in the United States than in other countries in the world. As a substitute, glucose may be used. This is found in grapes and in raisins and it is also produced in large quantities by the hydrolysis of starch and sold under the commercial name of corn syrup or Karo. This substance is entirely wholesome and may be freely employed in the place of sugar, which is scarce.

As to the use of alcoholic beverages, the question resolves itself into several factors. Alcohol gives a sham sensation of added force and in reality decreases the ability to do work. Alcohol is the greatest cause of misery in the world, and as Cushny has put it, if alcohol had been a new synthetic drug introduced from Germany, its importation would long since have been forbidden. On the other hand, good beer makes poor food taste well. It also frequently leads to overeating. The cure for bad food is to have our daughters taught how to cook a decent meal. After that we can talk about prohibition.

In some parts of the world whole nations are starving to death. In most countries of the world people are short of food. In America we have more food than in any other land, and we must, therefore, be careful in our abundance, saving it to the utmost, while, at the same time, conserving the safety of our own people.

[3] Walking.